Customers of China’s two largest mobile phone networks, China Mobile and China Unicom, have had their text-messaging service blocked after sending risqué texts, according to the state media.

It comes as the country is embroiled in a row with Google over cyber attacks. On Tuesday the internet giant, said it may quit China because of concerns about the country’s recent increase in censorship.

The Global Times, a government-run newspaper, said “everyone seems to be under watch”. Last year, the government vowed to suppress pornography on the internet and has now extended its campaign to mobile phones.

China Mobile is the world’s biggest mobile phone company, with over 508 million customers. Its network handles 1.7 billion text messages a day.

The latest development implies that Chinese censors have moved beyond monitoring of the internet and are now also spying on the country’s vast network of phones.

The newspaper interviewed a civil servant, who expressed reservations over the policy. “We have a lot of private things in our mobile phones. If they monitor the messages, a lot of private things would be leaked,” said the man, who was named only as Mr Cao.

The Southern Metropolis newspaper said a man from the Southern city of Dongguan recently had his phone blocked. China Mobile’s customer service informed the man that their computers had detected lewd words in his messages and that he would have to take his identity card to the local police station to reactivate the phone. He also had to furnish a letter guaranteeing that he would no longer disseminate inappropriate messages.

China Mobile said that the company was complying with demands from the police to report “illegal” text messages with content that included pornography, violence, fraud, suggestions of terrorism, instigations to crime and gambling.

The company said a single message that breached any of its filters would result in the blocking of the mobile phone involved.

Yesterday Microsoft said it no plans to pull out of China dashing hopes that the software giant would support its rival Google in its stand against Chinese censorship of the internet.

Asked if Microsoft had any plan to pull its business out of China, Steven Ballmer said “No.” before questioning the sudden urgency of Google’s complaints about attempts to hack Gmail accounts of human rights activists from inside China.

“I don’t understand how that [a Google pull-out] helps anything. I don’t understand how that helps us and I don’t understand how that helps China,” he said.

Google cited cyber attacks from within China as the final straw in a long-running battle against the Chinese authorities since setting up its Chinese operations in 2006.

However Mr Ballmer, whose company’s search engine Bing could benefit if Google surrenders its 30 per cent share of the Chinese search market, questioned the significance of the cyber attacks which Google detected in December and affected more than 30 major corporations.

“There are attacks every day. I don’t think there was anything unusual, so I don’t understand,” he said, “We’re attacked every day from all parts of the world and I think everybody else is too. We didn’t see anything out of the ordinary.”

The Obama administration has given full support to Google, demanding an 'explanation’ for the hacking attacks which it said raised 'very serious concerns’ about both freedom of speech and the trust needed to underpins a globalised economy..

“It seems to me that the principles that Google is trying to uphold are not just important in a moral or rights framework, but are also of very considerable economic importance,” said senior White Senior White House economic adviser Lawrence Summers on Thursday.

China has so far shown no signs of giving ground over Google’s demand to be allowed to operate in China uncensored, insisting that web controls are essential to maintain the “stability and harmony” of the Chinese nation.

Yesterday some of China’s most prominent human rights activists claimed that they had had their Google email accounts hacked.